The present invention relates to a masa foodstuff. In particular, the present invention relates to a masa foodstuff comprising a modified protein wherein the unmodified protein is native to corn.
Corn provides the base ingredient for many staple foodstuffs. For example, corn may be processed to produce masa. Masa is the raw material for production of products such as corn tortilla, soft tortilla, corn chips, tortilla chips, taco shells, tamales. Masa is produced by a nixtamalisation process (also called alkaline cooking process). The nixtamalisation process involves cooking corn which still carries its outer shell (the pericarp). The cooking is performed in an alkaline solution such as lime (calcium hydroxide) and generally is for 12 to 24 hours. The cooked product is then steeped and washed to produce nixtamal. The nixtamal is then stone-ground to a soft moist dough called masa.
For the convenience of a domestic user or for some commercial users, it is desirable to provide the dry flour, or instant tortilla flour, that is called masa harina. Certain known processes for making masa harina include U.S. Pat. No. 826,983 disclosing steeping corn in the traditional manner, followed by drying the kernels and grinding into flour. U.S. Pat. No. 987,560 teach a process for partially boiling corn in calcium hydroxide solution and then grinding the wet kernels into paste. Water is pressed from the paste, followed by drying of press cake in a heated chamber, followed in turn by grinding into flour. A similar process is disclosed in U.S. Pat. No. 1,262,144 where the amount of lime in water is one-half percent, and in U.S. Pat. No. 1,334,366 calls for molding of dough into small thin cakes which are dried and then ground into flour. A similar process is described in U.S. Pat. No. 2,584,893.
U.S. Pat. No. 2,704,257, U.S. Pat. No. 2,854,339 and U.S. Pat. No. 2,930,699 disclose steeping of corn in calcium hydroxide solution at a temperature well below the gelatinisation point of starch of the corn, followed by drying of the whole steeped corn in a hot airstream while simultaneously comminuting it to obtain a flour which has been dried at temperatures less than 74xc2x0 C. to a moisture content of not more than 10% by weight. The patents also describe apparatus for use in the drying and grinding steps.
U.S. Pat. No. 4,463,022 discloses a method for producing masa comprising the steps of placing the dry corn kernels in a vessel of boiling water and maintaining the water boiling for about five minutes. Heat is removed from the vessel, and the water and corn kernels are allowed to cool for about two hours under ambient conditions, bringing the temperature down to about 160xc2x0 F. The corn kernels are then further cooled and washed by establishing a low volume flow of cool tap water through the vessel for about an additional two hours. Following this treatment, the hulls of the kernels are broken by passing the kernels through a set of crushing rolls spaced apart about one-eighth of an inch. Thereafter, the mass of hull-broken kernels is entirely, hull and all, forced through a plate perforated as a sieve, the perforations being very small in relation to the size of the corn kernels. This produces a uniform and highly desirable masa product. The moisture content of the mass of material is desirably adjusted to about 50% by weight, either before or after the material is forced through the perforations.
After production masa may then be treated in a number of ways. The masa may be introduced into, for example, a tortilla mold or a tortilla sheeter. This is the traditional end use for the masa. In an alternative, the masa can be dried and milled into a xe2x80x9cshelf-stablexe2x80x9d flour product. The masa may be reconstituted from the flour product at a later stage and then formed into a food product, such as tortilla.
With regard to industrial implementation, typically masa is sold in the form of the dried masa or is formed into a final food product, such as a tortilla, which is then packed. In both of these aspects, one of the advantages of providing the product in this form is that the end user is freed of the need to prepare the nixtamal and masa from the corn constituent. The requirements for labour, energy and processing time for the end use are reduced. Moreover, the product is simple to use.
Limitations in supply chains, particularly in developing regions which predominantly consume masa based products, require that corn products, such as tortillas, should typically retain their properties for at least 7 days after production.
Additives to corn tortillas and their effects on storage stability are discussed in the prior art. For example, J. C. Yau et al., xe2x80x9cEffects of Food Additives on Storage Stability of Corn Tortillasxe2x80x9d, Cereal Foods World, May 1994, Volume 39, No. 5, 397-402 discusses the incorporation of vegetable and animal proteins, gums, emulsifiers, modified starches and polyols into nixamalised corn flour during processing. The rheological properties (rollability and pliability), machinability, moisture content, and organoleptic properties were evaluated. The properties of the tortilla were measured when the tortilla was cold. Since starch retrogrades under storage, it may be concluded that Yau et al. are concerned with the effects of starch in the tortilla. Yau et al. discuss that at least some of the disclosed additives may provide a gel network which improves the retention of steam and the extent of puffing of corn tortillas on cooking. Moreover, it is discussed that proteins in corn masa do not form a gel network.
Further prior art disclosures of additives to corn masa products are provided by WO 96/39864, WO 95/14397, and U.S. Pat. No. 3,655,385. WO 96/39864 relates to the production of xe2x80x9cfat freexe2x80x9d corn chips made from corn flour or masa. The chips contain (i) up to 50% masa, (ii) starch, protein or fibre and (iii) a filler. Component (ii) and (iii) are incorporated to reduce the fat content of the corn chips.
WO 95/14397 relates to extruding a cereal grain dough containing a gum such as carboxymethylcellulose (CMC) and an optional protein to provide a product for subsequent frying. The fried food product may be a corn chip. This document teaches that gums are incorporated to allow correct hydration of the starch component of the corn flour. WO 95/14397 relates to the extrusion of a cereal grainxe2x80x94an alkaline treatment step (nixtamalisation) of the grain is explicitly avoided.
U.S. Pat. No. 3,655,385 relates to the prevention of staling in tortillas containing a hydrophilic edible gum. Prevention of staling is said to be achieved by the water retention of the hydrophilic gum.
Whilst the prior art offers various additives which may alter the storage ability or handling characteristics of a masa foodstuff, the prior art teaching offers no solution to the problem of providing tortillas or masa flour which have both good storage stability and/or handling properties.
The present invention addresses the problems of the prior art
According to a first aspect of the present invention there is provided a process for the preparation of a modified masa foodstuff, the process comprising the steps of (i) preparing a masa by nixtamalisation of corn (ii) contacting a reducing agent or an enzyme with (a) the masa, and/or (b) the corn prior to nixtamalisation; such that a protein native to the corn is modified.
By the term xe2x80x9cnixtamalisationxe2x80x9d it is meant heating corn which still carries its outer shell (the pericarp) in an alkaline solution. Preferably the alkaline solution is an aqueous solution of lime or calcium hydroxide.
The present invention may provide a masa foodstuff having improved handling properties. For example when the masa foodstuff is a tortilla the present invention improves rollability of the tortilla. By the term xe2x80x9cimprove reliability of the tortillaxe2x80x9d it is meant achievement of a higher score than a control tortilla containing 0.5% CMC, when subjected to the Rollability Test described below. Yet further when the masa foodstuff is a tortilla the present invention improves foldability of the tortilla. By the term xe2x80x9cimprove foldability of a tortillaxe2x80x9d achievement of a higher score than a control tortilla containing 0.5% CMC, when subjected to the Foldability Test described below.
The present invention improves the interaction of proteins present in the corn. In the present specification by the term xe2x80x9cimproving the interactionxe2x80x9d or xe2x80x9cimprove(s) the interactionxe2x80x9d it is meant a higher degree of interaction when compared to an aspect not in accordance with the present invention. In other words in the present specification by the term xe2x80x9cimproving the interactionxe2x80x9d or xe2x80x9cimprove(s) the interactionxe2x80x9d it is meant a higher degree of interaction when compared to an unmodified protein.
In the present specification the term xe2x80x9ccornxe2x80x9d is analogous to the US terminology xe2x80x9cmaizexe2x80x9d. In the present specification by the term xe2x80x9ccornxe2x80x9d it is meant the seed or kernel of a corn or maize plant.
In the present specification by the term xe2x80x9cmodified proteinxe2x80x9d it is meant a protein which has been modified from its native state by a reducing agent or an enzyme.
In the present specification by the term xe2x80x9cnative to cornxe2x80x9d it is meant a protein which is present in complete corn.
The proteins in masa foodstuffs are not very interactive. The present invention improves protein interactions either to other proteins or to other components such as lipids and carbohydrate. Thus the handling properties of masa foodstuffs such as strength, elasticity, extensibility, rollability and foldability of tortilla may be improved.
Without being bound by theory it is believed that the properties of masa such as tortilla are enhanced by the present invention because of the effect of the present invention on the native protein of the corn. This is explained in further detail below.
A corn product may be studied under a microscope. It can be observed that the proteins present in an aqueous composition of the corn product tend to group together. This is often observed with proteins but is particularly the case with masa products because the alkaline solution of the nixtamalisation process encourages aggregation of the proteins.
We have found that by xe2x80x9copening upxe2x80x9d the proteins which group together the present invention achieves better interaction of the proteins which were native in the corn. The interaction may be improved between the modified proteins and other proteins or between the modified proteins and other constituents of the masa. This improved interaction may be achieved by modifying the proteins with a reducing agent or an enzyme, such as a protease.
This theory is supported not only by our visual studies of the proteins but also by subsequent studies of the strength of tortillas made from corn products containing modified proteins. If an aggressive enzyme, such as an unspecific protease with high activity, is contacted with the corn product, the proteins are modified to such an extent that there is insufficient interaction between them. The strength of the tortilla then diminishes and the tortilla cannot be readily handled. For the reasons discussed below, this may be because the proteins are modified to an extent that substantially no high molecular weight proteins are available to provide an interacting network.
Preferably, the unmodified protein which is modified and/or the protein the interaction of which is improved, is a high molecular weight protein or an aggregate of proteins wherein the aggregate has a high molecular weight. High molecular weight proteins or high molecular weight protein aggregates are important in providing a structure which contributes to the properties of a foodstuff such as a tortilla. Thus modification and/or improvement of the interaction of such a high molecular weight protein or high molecular weight protein aggregates is particularly advantageous. The lesser importance of modification of low molecular weight proteins or low molecular weight protein aggregates is exemplified by our studies described above using an aggressive enzyme, such as an active and unspecific protease. The protease was found to modify the high molecular weight protein to such an extent that the strength of the tortilla diminishes and the tortilla cannot be readily handled.
In the present specification by the term xe2x80x9chigh molecular weight proteinxe2x80x9d or xe2x80x9chigh molecular weight protein aggregatexe2x80x9d it is meant a protein or a protein aggregate having a molecular weight of at least 100 kDa. This is preferably measured with a Malvern.
The protein may be modified with an enzyme or a reducing agent. Both modification agents have advantages. By the term xe2x80x9cmodifiedxe2x80x9d in respect of the protein native to corn it is preferably meant that the conformation of the protein is changed. In one aspect by the term xe2x80x9cmodifiedxe2x80x9d it is preferably meant that a peptide or disulphite bond of the protein is cleaved.
Enzymes may be contacted with the corn product, such as the nixtamal, the masa or the masa flour. The enzyme modifies the protein native to the corn. The activity of the enzyme may then be readily terminated by heating the enzyme. Heating will denature the enzyme and therefore the activity thereof will cease.
The use of an enzyme is particularly advantageous because denatured enzyme need not be disclosed in a food ingredient listing after denaturation. Food labeling regulations consider enzymes to be processing aids. Denatured enzymes need only be declared as protein.
The activity of reducing agents is easier to control than that of enzymes. However, the reducing agent must be separated from the corn containing food material after contact therewith or, if it remains in the foodstuff, it must be declared in an ingredients list.
Typical enzymes may be selected from proteases such as disulfide isomerase and other enzymes that act on disulfide bonds, bacterial proteases such as GRINDAMYL(trademark) PR 41, and GRINDAMYL(trademark) PR 43, fungal proteases such as GRINDAMYL(trademark) PR 59 (a proteolytic enzyme complex produced from Aspergillus oryzae), and mixtures thereof, including mixtures of bacterial and fungal proteases such as GRINDAMYL(trademark) PR 46. Each of GRINDAMYL(trademark) PR 41, GRINDAMYL(trademark) PR 46, GRINDAMYL(trademark) PR 43, and GRINDAMYL(trademark) PR 59, are available from Danisco Ingredients, Denmark.
Preferably, the enzyme is a protease. A proteases may be selected such that a suitable degree of modification of a native corn protein is provided.
Typical reducing agents may be selected from L-cystein, metabisulfite, inactivated yeast extract (glutathione), derivatives and mixtures thereof.
Typically the masa or the corn may be contacted with the enzyme or reducing agent for 5 to 20 minutes, or in one aspect 10 to 20 minutes. This period of contact is usually sufficient to modify the proteins native to the corn to a sufficient degree such that improved interaction between the modified native protein occurs.
In preferred aspect, the present invention may further improve the interaction between native corn proteins and other constituents of the foodstuff such as other native corn proteins or modified corn proteins, lipids or carbohydrates by the addition of a protein matrix forming constituent to the foodstuff/food material. These matrix forming constituents may be selected from non-native protein, including whey protein, bovine serum albumin (BSA), gluten; emulsifiers such as citric acid, including CITREM LR 10, available from Danisco Ingredients, Denmark; hydrocolloids including gums, carboxymethylcellulose (CMC), carrageenan, guar gum, pectin; and mixtures thereof.
Typical emulsifiers may be selected from include CREMODAN(copyright) (manufactured and distributed by DANISCO INGREDIENTS) including CREMODAN(copyright) DC, CREMODAN(copyright) MOUSSE, CREMODAN(copyright) SE, CREMODAN(copyright) SI, CREMODAN(copyright) SIM, CREMODAN(copyright) ) SL, CREMODAN(copyright) TEF; GRINDSTED(trademark) (manufactured and distributed by DANISCO INGREDIENTS), including GRINDSTED(trademark) BK, GRINDSTED(trademark) CITREM, GRINDSTED(trademark) ES, GRINDSTED(trademark) FF, GRINDSTED(trademark) GA, GRINDSTED(trademark) PS such as GRINDSTED(trademark) PS 100, GRINDSTED(trademark) PS 200, GRINDSTED(trademark) PS 300, GRINDSTED(trademark) PS 400, GRINDSTED(trademark) WP; RECODAN(trademark) (manufactured and distributed by DANISCO INGREDIENTS); RYLO(trademark) (manufactured and distributed by DANISCO INGREDIENTS), including RYLO(trademark) AC, RYLO(trademark) Cl, RYLO(trademark) LA, RYLO(trademark) MD, RYLO(trademark) MG, RYLO(trademark) PG, RYLO(trademark) PR, RYLO(trademark) SL, RYLO(trademark) SO, RYLO(trademark) TG; DATEM (diacetyl tartaric acid esters of mono-diglycerides), e.g., PANODAN(copyright) (manufactured and distributed by DANISCO INGREDIENTS), CITREM (citric acid esters of monoglycerides) and/or sodium stearoyl lactylate, derivatives and mixtures thereof.
Preferably, the hydrocolloid is selected from CMC, carrageenan, guar gum, pectin and mixtures thereof. In a highly preferred aspect the hydrocolloid is at least a mixture of CMC and carrageenan.
Preferably the hydrocolloid is carrageenan.
Thus in a further aspect there is provided a masa foodstuff comprising corn, wherein the masa foodstuff further comprises carrageenan.
Carrageenan either alone or in combination with other hydrocolloids such as CMC has given positive effects in trials. This may be because of interaction with proteins.
It is to be noted that the combination of carrageenan with an enzyme, such as a protease, or a reducing agent maintains the water holding capacity benefits from the hydrocolloids and network strengthening effect and additionally improves the surface texture of the tortilla.
The present invention is further advantageous because it allows for the use of strong corn or flour from hard milling corn originating from North America, in particular the US. US flour contains protein which has weak interactions due to their compact structure. Thus the present invention allows for the use of this corn in preparing masa foodstuffs in which the handling properties of the product would normally prohibit the use of US flour.
The present invention also provides nutritional advantages. Corn protein is not absorbed by the human digestive tract. By xe2x80x9copening upxe2x80x9d the protein structure of corn products, the nutritional value of the masa foodstuffs is increased. Nutritional value is often improved by manufacturers by the addition of soya protein or whey protein to the masa product. Thus, not only does the present invention improve the nutritional value of the masa foodstuff, it also provides an economic benefit because the addition of further protein material is reduced or rendered unnecessary.
It is also believed that a further advantage of the invention is that modified proteins with improved interaction seal the surface of the foodstuff such as a tortilla resulting in a softer and smoother surface.
Preferably, the masa foodstuff of the present invention is selected from corn tortilla, soft tortilla, corn chips, tortilla chips, taco shells, tamales, derivatives and mixtures thereof. More preferably the foodstuff is a tortilla.
In a further aspect of the present invention there is provided a masa foodstuff obtainable or obtained by a process as defined herein.
In a further aspect of the present invention there is provided a masa foodstuff comprising a modified protein wherein the unmodified protein is native to corn.
In a further aspect of the present invention there is provided use of a reducing agent or an enzyme to improve the interaction of a protein in a masa foodstuff, wherein the protein is native to the corn.
In summary, the present invention provides a masa foodstuff in which the interaction of native proteins is improved such that handling and/or texture of the masa foodstuff is improved. Native proteins are modified in such a way that more interactive sites of the proteins are exposed for interactions. In the laboratory effects has been seen using reducing agent such as L-cystein, metabisulfite and inactivated yeast extract (glutathione).
Alternatively enzymes, for example proteases, may be used. Proteases may affect the strength and flexibility of the tortilla in a negative way (to much proteolysis) or in a positive way (mild proteolysis, just opening the protein aggregates). It is possible that the screening of specific proteases may be used to select proteases which can give desired and/or improved results.
Thus in a further aspect there is provided a method for determining the degree of modification of a native corn protein by a protease, wherein the method comprises: (a) contacting a protease of interest with a native corn protein; and (b) determining the extent to which the protease modifies the protein (if at all).
Native corn proteins are not very active compared to proteins present in other food material, for example gluten proteins. The present invention improves the interaction between native proteins and thus improves the properties of masa foodstuffs, such as tortilla. This is achieved by modifying the native protein.
Without being bound by theory, it is believed that the present invention assists in incorporation of carbohydrates such as aribinoxylans and/or lipids in the network of native proteins.
In a preferred aspect gluten may also be incorporated in the masa foodstuff of the present invention. When the masa foodstuff of the present invention is a flour, gluten is preferably added in an amount of 0.1 to 1.5% based on the total weight of the flour. More preferably, gluten may be added in an amount of approximately 0.3 to 1% based on the total weight of the flour. Yet more preferably, gluten may be added in an amount of approximately 0.5% based on the total weight of the flour.
The applicant has found that gluten particularly improves interaction between native proteins and yet further improves the interaction between native proteins and other flour components such as aribinoxylan.
In a further preferred aspect, zein protein is also incorporated in the masa foodstuff of the present invention. Zein protein which is present in the corn outer endosperm is particularly vulnerable to the lime cooking process of nixtamalisation. If zein protein is obtained from an alternative source which is not subjected to lime cooking and added to the masa foodstuff of the present invention, improved properties are observed. Preferably, the zein protein is solubilised from the outer endosperm of corn, freeze dried and then, as described above, added to the foodstuff.
Preferably, a protein matrix forming constituent is also incorporated in the masa foodstuff of the present invention. The matrix forming constituent is used to improve interaction between native corn proteins and other native corn proteins.
In some aspects it has been found that the, proteins, emulsifiers, hydrocolloids may be used in place of as well as in addition to the enzyme or reducing agent of the present invention. Thus in a further aspect the present invention provides use of a substance selected from reducing agents, enzymes, proteins, emulsifiers, hydrocolloids, derivatives and mixtures thereof to improve the interaction of a protein in a masa foodstuff, wherein the protein is native to the corn.
Preferably, the viscosity of an aqueous suspension of the masa foodstuff of the present invention, more preferably a tortilla corn product, is from 5 to 12 cP, more preferably from 5 to 8 cP. Preferably the viscosity is from 6 to 7 cP.